Things we know about obito
- obito somehow gained ms, and we know that in order to gain ms you must kill someone you love/are closest to
- obito loved Rin but we do not know how she died
- the latest manga shows that obito becomes madaras apprentice, a man who willingly killed his closest friend AND his own brother in order to gain more power.
- since obito did not return to konoha, madara could have convinced him that he must kill Rin in order to gain more power
- obito could be blaming kakashi for not protecting her from him.

- I'm not saying this is what happened, just a theory and I'd like to hear what you guys think

Honestly, it could also be theorized that madara trained obito and became his father figure and master, then forced obito to kill him in order to gain his ms, which would also explain how madara died.

What do you think?